1. Field of the Invention
The present invention relates to a method for manufacturing a liquid crystal display (LCD) device, and more particularly, to a transflective (reflective-transmission) type liquid crystal display (LCD) device and method for manufacturing the same to improve yield by decreasing the number of masks.
2. Discussion of the Related Art
With development of information in society, demands for various display devices have increased. Accordingly, many efforts have been made to research and develop various flat display devices such as liquid crystal displays (LCD), plasma display panels (PDP), electroluminescent displays (ELD), and vacuum fluorescent displays (VFD). Moreover, some species of the flat display devices have already been applied to displays of various equipment.
Among the various flat display devices, the LCD device has been most widely used due to advantageous characteristics of thinness, lightness in weight, and low power consumption. Thus, LCD devices are used as substitute for Cathode Ray Tubes (CRT). In addition to mobile type LCD devices, such as displays for notebook computers, LCD devices have been developed for computer monitors and televisions to receive and display broadcasting signals.
Despite various technical developments in LCD technology with applications in different fields, research for enhancing the picture quality of LCD devices has been, in some respects, lacking as compared to other features and advantages of LCD devices. To use LCD devices in various fields as general displays, a key to developing LCD devices depends on whether an LCD devices can achieve a high quality picture, including high resolution and high luminance with a large-sized screen while still maintaining lightness of weight, thinness, and low power consumption.
LCD devices display images or pictures by controlling light transmittance with an electric field applied to liquid crystals having a dielectric anisotropy.
A LCD device is different from display devices such as an electroluminescence (EL) device, a cathode ray tube (CRT) and a light emitting diode (LED) device that emits light itself in that the LCD device makes use of ambient light as a light source.
LCD devices are classified into two different types: a transmission type LCD device and a reflection type LCD device, according to the light source employed. A transmission type LCD device has a backlight as a light source at the rear of an LCD panel, so that a transmission type LCD device can display a picture image in low light surroundings by controlling light transmittance according to the alignment of liquid crystals. However, the transmission type LCD device has problems in that it requires relatively high power consumption. Meanwhile, a reflection type LCD device makes use of ambient light as a light source, thereby having a relatively small amount of power consumption. However, a reflection type LCD device has problems in that it cannot display a picture image in low light surroundings such as found in cloudy or unclear weather.
In order to solve the problems of both the transmission and reflection types of LCD device, a transflective (reflective-transmission) type LCD device has been proposed. The transflective type LCD device can be formed as a reflection type or a transmission type of LCD device, as needed.
Hereinafter, a related art transflective type LCD device and method for manufacturing the same will be described with reference to the accompanying drawings.
FIG. 1 is a plan view illustrating the related art transflective type LCD device.
As shown in FIG. 1, a plurality of gate lines 11 are formed on a lower substrate 10 at fixed intervals, and a plurality of data lines 12 are formed for being in perpendicular to the gate lines 11 at fixed intervals, thereby defining a plurality of pixel regions. Meanwhile, a storage line 19 is formed parallel to the gate line 11 at a predetermined interval from the gate line 11, thereby crossing the pixel region P and an active layer 14.
In the pixel region P, defined by crossing the gate and data lines 11 and 12 to each other, a transparent electrode 16 is formed in a matrix type. Also, a thin film transistor is formed to transmit a signal of the data line 12, being switched by a signal of the gate line 11, to the transparent electrode 16.
The thin film transistor includes a gate electrode 13, a gate insulating layer (not shown), the active layer 14, a source electrode 15a and a drain electrode 15b. The gate electrode 13 extends from the gate line 11. The gate insulating layer is formed on an entire surface of the lower substrate 10. Also, the active layer 14 is formed on the gate insulating layer above the gate electrode 13. The source electrode 15a extends from the data line 12, and the drain electrode 15b is opposite to the source electrode 15a. In this state, the drain electrode 15b is electrically connected with the transparent electrode 16 through a contact hole 17.
Also, a reflective electrode 18 is formed at a predetermined portion of the pixel region to be overlapped with the transparent electrode 16.
Meanwhile, the lower substrate 10 having the aforementioned structure is attached to an upper substrate (not shown) with a gap therebetween.
At this time, the upper substrate includes a black matrix layer, a color filter layer of R/G/B, and a common electrode (not shown). The black matrix layer has openings corresponding to the pixel regions formed on the lower substrate 10, and prevents light. Also, the color filter layer of R/G/B is formed to obtain various colors. The common electrode drives liquid crystal with the transparent electrode 16 (reflective electrode).
The lower substrate 10 is attached to the upper substrate with a gap therebetween by spacers. After that, the lower and upper substrates are bonded to each other by a sealant, and then liquid crystal is injected between the lower and upper substrates.
FIG. 2 is a cross-sectional view illustrating the related art transflective type LCD device taken along line I–I′ of FIG. 1.
As shown in FIG. 2, the related art transflective type LCD device includes an insulating substrate 21, a buffer layer 22, an active layer 23, a gate insulating layer 25, gate and storage electrodes 26a and 26b, source/drain impurity regions 27, an insulating interlayer 28, source and drain electrodes 30a and 30b, a passivation layer 31, a reflective electrode 32, and a transparent electrode 34.
The insulating substrate 21 is formed of a reflection region and a transmission region. The buffer layer 22 is formed on the insulating substrate 21, and the active layer 23 is formed on a predetermined portion of the buffer layer 22. Then, the gate insulating layer 25 is formed on an entire surface of the insulating layer 21 including the active layer 23. The gate and storage electrodes 26a and 26b are formed on the gate insulating layer 25 corresponding to the active layer 23. The source/drain impurity regions 27 are formed on the active layer 23 at both sides of the gate electrode 26a. Also, the insulating interlayer 28 is formed on the reflection region of the insulating substrate 21, and has a first contact hole for exposing predetermined portions of the source/drain impurity regions 27. The source and drain electrodes 30a and 30b are connected with the source/drain impurity regions 27 through the first contact hole. The passivation layer 31 is formed over the reflection region of the insulating substrate 21, and has a second contact hole for exposing a predetermined portion of the drain electrode 30b. After that, the reflective electrode 32 is formed over a predetermined portion of the passivation layer 31. The transparent electrode 34 is overlapped with the reflective electrode 32, and connected with the drain electrode 30b through the second contact hole so that the transparent electrode 34 is formed over the transmission region of the insulating substrate 21.
At this time, the transparent electrode 34 is overlapped with the reflective electrode 32, and is formed in the pixel region for crossing the gate line (11 of FIG. 1) to the data line (12 of FIG. 1).
FIGS. 3A to 3H are cross-sectional views illustrating the related art transflective type LCD device taken along line I–I′ of FIG. 1.
As shown in FIG. 3A, the buffer layer 22 is formed over the insulating substrate 21, and an amorphous silicon layer is formed on the buffer layer 22. Subsequently, laser or heat is applied to the amorphous silicon layer so that a polycrystalline silicon layer is formed. Then, the polycrystalline silicon layer is selectively removed by photolithography, whereby the active layer 23 is formed.
As shown in FIG. 3B, a photoresist 24 is deposited on the entire surface of the insulating substrate 21 including the active layer 23. After that, the photoresist 24 is patterned by exposure and developing process, thereby defining a capacitor region. Then, conductive impurity ions are injected into the exposed active layer 23 by using the patterned photoresist 24 as a mask. The conductive impurity ions are injected to the active layer 23 since the active layer 23, the polycrystalline silicon layer, has no conductivity. Because of injection of the conductive impurity ions, the active layer 23 obtains conductivity so that can be used as a lower electrode of a storage capacitor.
As shown in FIG. 3C, after removing the photoresist 24, the gate insulating layer 25 is formed over the entire surface of the insulating substrate 21 including the active layer 23. Then, a low-resistance metal layer is formed on the gate insulating layer 25. The metal layer is selectively removed by photolithography, thereby forming the gate electrode 26a and the storage electrode 26b at a predetermined interval from each other on the gate insulating layer 25 corresponding to the active layer 23.
The gate insulating layer 25 is formed by depositing silicon oxide or silicon nitride in a CVD (Chemical Vapor Deposition) method. The metal layer is formed in a method of depositing a conductive metal layer such as aluminum Al, aluminum alloy AlNd, chrome Cr, tungsten W or molybdenum Mo by sputtering.
Subsequently, n-type or p-type impurity ions are selectively doped on the entire surface of the insulating substrate 21 by using the gate electrode 26a as a mask. Thus, the source/drain impurity regions 27 are formed on the active layer 23 at both sides of the gate electrode 26a. 
As shown in FIG. 3D, the insulating interlayer 28 is formed over the entire surface of the insulating substrate 21 including the gate electrode 26a. Then, the insulating interlayer 28 is selectively removed to expose the predetermined portions of the source/drain impurity regions 27 by photolithography, thereby forming the first contact hole 29. The insulating interlayer 28 is formed of inorganic insulating material such as silicon nitride or silicon oxide, or organic insulating material having low dielectric constant such as acrylic organic compound, Teflon, BCB, cytop or PFCB.
As shown in FIG. 3E, the metal layer is deposited on the entire surface of the insulating substrate 21 including the first contact hole 29. Then, the metal layer is selectively removed by photolithography. Thus, the source and drain electrodes 30a and 30b are electrically connected with the source/drain impurity regions 27 through the first contact hole 29. The metal layer is formed of metal such as aluminum Al, copper Cu, tungsten W, chrome Cr, molybdenum Mo, titanium Ti or tantalum Ta, or molybdenum alloy such as MoW, MoTa or MoNb. After that, the insulating interlayer 28 corresponding to the transmission region is selectively removed by photolithography.
As shown in FIG. 3F, the passivation layer 31 of organic insulating material is formed on the entire surface of the insulating substrate 21 including the source and drain electrodes 30a and 30b. Then, the passivation layer 31 corresponding to the transmission region is selectively removed by photolithography.
Meanwhile, the surface of the passivation layer 31 may be selectively removed by photolithography, so that the passivation layer 31 has an uneven surface. Next, an opaque metal layer is deposited on the entire surface of the insulating substrate 21 including the passivation layer 31. Subsequently, the opaque metal layer is selectively removed by photolithography to form the reflective electrode 32.
As shown in FIG. 3G, the passivation layer 31 is selectively removed to expose a predetermined portion of the drain electrode 30b, thereby forming the second contact hole 33.
As shown in FIG. 3H, a transparent metal layer is deposited on the entire surface of the insulating substrate 21 including the second contact hole 33. Then, the transparent electrode 34 completely covering the reflective electrode 32 is electrically connected with the drain electrode 30b by photolithography.
The metal layer is formed of ITO (indium-tin-oxide), IZO (indium-zinc-oxide) or ITZO (indium-tin-zinc-oxide), Al, AlNd, Cr or Mo by the CVD method or sputtering. An insulating layer may be formed between the transparent electrode 34 and the reflective electrode 32.
FIG. 4 is an expanded cross-sectional view illustrating ‘A’ portion of FIG. 3G.
As shown in FIG. 4, the passivation layer 31 has an uneven surface, and the reflective electrode 32 is formed on the passivation layer 31 including its uneven surface.
The reflective electrode 32 has an uneven surface according to the uneven surface formed on the passivation layer 31. As a result, when incident light is reflected on the reflective electrode 32, and is emitted again, it is possible to concentrate the light being incident at different angles to a predetermined angle.
However, the related art transflective type LCD device and method for manufacturing the same has the following disadvantages.
First, an additional mask is used when injecting the conductive impurity ions into the active layer so as to obtain conductivity in the active layer that is used as the lower electrode of the storage capacitor, thereby increasing manufacturing cost.
Also, the related art transflective type LCD device and method for manufacturing the same require masks for selectively removing the insulating interlayer exposing the predetermined portion of the drain electrode, and defining the transmission region. Thus, the number of masks is increased in manufacturing process steps, thereby increasing manufacturing cost.